Raw & Organic Silk: Facts behind the Fibers

Silk, the “Queen of Fiber”. Darling of the haute couture set for the luxurious feel and drape; villain of vegans and PeTA for the doomed silk worm who labors to spin the fine fiber and then is gassed or boiled alive. Even though silk is a natural fiber that has been woven into fabric to dress China’s Empresses since 2900 BC (back when the entire world population was only 15 million people), silk is just starting to be proclaimed as a “natural” fabric, but how organic, sustainable, ethical and healthy is silk?

“With time and patience the mulberry leaf becomes a silk gown” – Ancient Chinese Proverb. The finest, most desirable silk comes from the mulberry silkworm, which is actually a caterpillar and not a worm. Known as the Bombyx mori by entomologists, the mulberry silk worm is a fascinating but tragic bundle of insect life. Raised by professional keepers in China on trays of mulberry leaves a thousand years before the Roman Empire when wild tribes were roaming Europe living in stick and mud huts, the mulberry silkworm has been totally domesticated and can not live without humans for their care and feeding. There are no wild silkworms or Bombyx mori moths that roam and feed in the wild.

Across several thousand years of captive breeding, the Bombyx mori evolved into a blind moth that cannot fly and lives only a few days during which it lays about 500 eggs and then dies within four or five days. The silkworm moth has even lost the ability to eat because of undeveloped structures within their mouth.

A Bombyx mori egg hatches in 10 days and becomes a larva – the silkworm caterpillar. The silkworm larva will voraciously eat mulberry leaves almost non-stop for 35 days increasing its weight 10,000 times from a tiny speck to a chubby grub. Silkworms are very delicate and will go off their feed from loud noises, temperature fluctuations of more than a few degrees above or below 76 degrees, or even strong smells.

When it is full grown, the silk worm (called a pupae) climbs a twig and begins spinning a cocoon. This stage of silkworm life is called pupating. The silkworm produces a fibroin protein compound in two salivary glands called sericteries that is mixed in the mouth of the silkworm with a gooey substance called sericin and forced out through an opening in the silkworm’s under lip. When this stream of sticky fluid comes into contact with air, it solidifies and becomes a continuous strand of silk that becomes the silkworm’s cocoon. The openings in the under lip of the silkworm are called spinnerets and the process is very similar to spinning manmade “natural” fibers such as viscose rayon or lyocell Tencel … except that it is air for silk rather than an acid bath for viscose and lyocell that causes the fibers to solidify. The silkworm will spin a thousand yards of silk fiber in three days to form its completely enclosed cocoon. To fashion its cocoon, the silkworm will continually weave its head in a figure eight pattern an estimated 300,000 times while continually spinning and secreting its silk fiber. The cocoon will be the silkworm’s home for sixteen days as it morphs from a chubby grub to a furry, winged moth. What an incredible marvel of Nature’s intelligence!

But here the story turns down. When the transformation is complete, the newly formed Bombyx mori moth secretes an alkali fluid that begins to dissolve a hole in the cocoon so that the moth can emerge. The silk farmers do not want their silk cocoons damaged so they kill the worms by tossing the cocoons into boiling water or hot ovens before they transform into moths and emerge from their cocoons. A small percentage of silkworms in cocoons are left to live so that a few moths will emerge to lay the next generation of silk machines. The sightless, flightless and toothless moth will mate almost immediately after emerging from the cocoon and lay 500 silkworm eggs during their first 4 or 5 days and then die. Total lifespan of the Bombyx mori is about 70 days for those lucky few who are allowed to live and reproduce and about 60 days for those unfortunate ones who are sacrificed for that fabulous Italian silk scarf from Elizabetta or Missoni 'Dianes' Lotus Print Dress ($2,935) from Nordstrom.

A hugely developed industry, called sericulture, has developed around the raising of silkworms for the production of silk. Silk worms are raised by large corporate silk worm farmers and hobbyists all over the world. Sericulture companies like Sericulum sell and ship all that the silk grower enthusiast needs from Bombyx mori ova (silkworm eggs) in an incubation dish to handling tools. Silkworms eat only mulberry leaves and you supply your own.

One silkworm produces very little useable silk. One acre of mulberry trees produces enough foliage to feed silkworms that create 178 pounds of cocoons which can be unraveled into 35 pounds of raw silk. The mulberry leaves are a renewable and sustainable crop as the trees produce year after year. One mature mulberry tree will produce enough foliage for 100 silkworms. The Bombyx mori silkworm is univoltine which means that they only produce one batch of eggs annually. When the eggs are laid, they enter a diapausal state of suspended development (hibernation), often induced by refrigerating the eggs for nine months. The silk worm farmers can induce the eggs to hatch at a commercially convenient time.

The modern Silk Road. To continue the journey from the silkworm egg to the display rack in Nordstrom or Neiman Marcus, dropping the cocoon in hot water not only kills the silkworm, but also dissolves the sticky sericin coating the silk fibers and holding the shape of the cocoon. Silk workers gently dry and brush the outside of the cocoon to find the end of the silk fiber that made the cocoon. The cocoon is carefully unraveled and wound around a spool. Five to ten individual silk fibers from cocoons are wound together to form one silk thread and several silk threads are wound together to form a yarn of silk. This is raw silk, just pure silk fibers without any chemicals or treatments added, although sometimes the raw silk fibers will be soaked in a 1% hydrogen peroxide solution for a few hours to refine the creamy color. Organic and sustainable certification organizations are working on standards for organic silk but they have not yet been finalized and adopted.

Up to this point in our journey down the modern Silk Road, our spool of raw silk threads could easily be produced to comply with emerging sustainable and organic standards for silk and be manufactured into silk eco-fashion and organic clothing … except for this little problem – a 3 inch ethical problem – the Bombyx mori silkworm that is gassed, steamed, or boiled alive to prevent them from escaping from their cocoon as a moth by dissolving a hole in the silk cocoon. To make one pound of the finest silk, 2600 silkworms must die.

Peace Silk or Vegetarian Silk. Fortunately for those who love the feel, luster and exceptional fabric properties of silk, there are other more ethical options. Some Bombyx mori silk producers allow the moths to emerge from the cocoon and then salvage the damaged cocoons. Because the one continuous silk fiber woven by the silkworm has been broken into many smaller strands by the emerging moth, the cocoon is degummed to remove the sericin and then spun like other fibers such as cotton or hemp rather than being reeled onto spools of one continuous silk strand. Because of the more humane harvesting of these silk cocoons, this silk is often called peace silk or vegetarian silk. This silk is slightly discolored by the alkaline solution secreted by the moth to create the hole, and the peace silk is not as strong and has a slightly different look and feel to the knowing designer or connoisseur than conventional Bombyx mori silk. Because the peace silk is spun as a fiber rather than reeled as a thread, it produces a fabric that is warmer and softer. 

Ahimsa silk is also peace silk.  Ahimsa peace silk often comes from the Eri Silk Moth and the Tassar moth and comes mostly from India.  The Ahimsa Peace Silk project in India is working to help develop the peace silk industry in India, train local artisians in the manufacturing of peace silks and raise global awareness for ahimsa peace silks.

Wild Silks. The Bombyx mori silkworm is not the only silkworm that spins a silk cocoon that can be used to produce silk fabric for silk clothing. There are many species of wild silk caterpillars that produce silk cocoons used in the production of silk fabrics, sometimes called “wild silks” or “peace silks” because the silk caterpillars are allowed to live complete and natural lives in the wild without being sacrificed for fashion. Most wild silkworms are multivoltine, which means that they produce cocoons several times during the year rather than just once a year like the Bombyx mori.

These wild caterpillars spin a silk that is different in texture and color from the domesticated Bombyx mori and the wild silk cocoon strands are shorter because they come from cocoons that have been damaged by the wild silk moth’s emergence from the cocoon. One of the highly desirable properties of the Bombyx mori silk fibers due to the unique structure of their fibroin protein is their exceptional ability to absorb dyes; wild silk caterpillars secrete a slightly different protein structure and their silk fibers tend to not accept dyes as well.

Exquisitely patterned wild silk fabrics are hand loomed in Thailand from the Saturniidae silk worm, and throughout India from a variety of wild silk caterpillars. One region of India that is especially noted for its exceptional and unique silks is the far northeastern state of Assam, which borders Bangladesh. Assam produces three different types of silk that are collectively known as Assam silk but which vary greatly in appearance. The Assam silks are Muga, Eri and Pat.

Muga (from the semi-domesticated silkworm Antherea assamensis) is renowned for its glossy fine texture, durability and natural golden amber glow. Reputed to be the second most costly fabric after Pashmina, Muga silk looks like spun gold and for 600 years only the royal families of Assam where allowed to wear muga silks. The golden hue increases with time and washing.  Muga silk is naturally stain-resistant and is never bleached or dyed. Muga silk fabric is naturally organic and untouched by chemicals, but it is not a “peace” or “vegetarian” silk because the silkworm is killed before it can emerge from the cocoon. Like cotton and silk, fashion is a blending of compromises.

Eri (from the domesticated silkworm Philosamia rinini) is a fine silk that is almost as white in color as the Bombyx mori silks. Even though Eri is spun from the cocoons of domesticated silkworms, it is a “peace silk” because the Antherea assamensis silk caterpillars are not destroyed in the cocoon but are allowed to emerge as moths and live a full lifecycle.  Because the Eri silk fibers are more uneven and the cocoons are damaged when the moth emerges, Eri silk is spun rather than reeled. Eri silk has the look of wool mixed with cotton but the feel and softness of silk. Muga and Eri silks are from silkworms that are only found in the Indian state of Assam.

Indigo Handloom, a small eco-fashion company bursting with energy and creativity, is developing a bridge between the ancient handlooming cottage industry found throughout rural India and contemporary modern Western cultures. With eco-design and sales offices in NYC, Indigo Handloom works closely with a small, select community of handloom artisans in India to create scarves of the most exquisite quality and design. They offer a number of timelessly beautiful Muga and Eri silk scarves that were crafted on ancient handlooms, many sitting outside small cottages where the artisan weavers can be near their young children.

The handloom industry in India employs 6,500,000 people and makes 23% of total cloth produced in India. Handlooming forms an important part of the rich cultural heritage of India and the skilled craftsmen weave the rich cultural heritage of India into garments of astounding beauty, complexity and simplicity – unifying opposites as only the harmonizing tradition of India can. Handlooming in India is a critical component of sustainable development in poor, rural regions. Handlooms are environmentally friendly with no external energy requirements so the energy impact is near zero, but the handloom industry is endangered by WTO policies that favor the large, globalized, powerloom textile companies.  Companies such as Indigo Handloom, under the vision of Smita Paul, are providing these local weavers with a venue for bringing their exquisite, eco-friendly fashions to Western markets.

Is silk organic, sustainable, ethical, healthy? The quick answer is that silk can be but the consumer must be aware and ask the right questions when shopping. Silk, like other protein fibers coming from living beings such as sheep and alpacas, can easily be created according to organic guidelines as they begin to be approved. And many silk fibers are probably already being produced in an organic environment, especially those produced in smaller villages and rural environments. To boost productions and improve efficiencies, large corporate farms will typically use heavy chemicals.

In the same way, the raising of domesticated silkworms and the life of wild silkworms is, by nature, sustainable. Silk fabric when produced by weavers on handlooms has a near zero energy footprint and satisfies most of the guidelines for sustainable fabric production. Silk produced in large powerloomed textiles factories must be evaluated on a company-by-company basis to determine their sustainability.

Ethical silk. Evaluating the ethics of silk is always a more complex and more personal question. Animal rights organizations are concerned about the destruction of several thousand domesticated silkworms to produce one pound of silk. Labor rights and Fair Trade organizations are concerned about the exploitive low wages often paid to silk textile workers.

Healthy Silk. While being a comparatively healthy and organic natural fiber, silk, like other fibers containing protein chains such as wools and even latex, is an allergen for some people. Silk allergies can cause asthma or allergic rhinitis with symptoms of runny nose and itchy eyes that are similar to hay fever. Medical researchers have found a wide variety of causes for a small number of people experiencing silk allergies: some are allergic to wild silk, some to domesticated silk, and some to micro-fine dust that can be given off by spun silk. Often, the allergies are traced to the diet of the silk worm – such as mulberry or oak leaves – which influence the protein chains found in the silk strands produced by the silk worm.

Some silk allergies come from excessive sericin in silk that has not been adequately degummed. Sericin is a complex protein produced by the silkworm that is sticky and coats the outside of the silk strand over the fibroin protein core. During the processing of the silk cocoon strands into silk threads, the silk workers use boiling hot soapy water that is slightly alkaline to degum the silk strands by dissolving much of the outer sericin layer. The waste silk, also called silk noil, from damaged cocoons and broken strands is often used as filling in silk duvets and lower quality spun silk fabrics. Sometimes the waste silk / silk noil is not sufficiently degummed resulting in excess sericin in the products that can result in silk allergic reactions for some people.

This process of degumming is also called scouring and is the first step in preparing silk for dyeing. Scouring and removing the sericin coating allows dyes to more easily penetrate the silk fibers. After scouring, silk is often bleached – sometimes with sulfur fumes to remove blemishes and leave the silk a uniform creamy color in preparation for dyeing.

Dyed Silk. As with any fabric, the dyeing of silk can also create health problems for people with chemical sensitivities and MCS. Because silk fibers are highly absorptive, Bombyx mori silk takes dyes exceptionally well and is one reason for the brilliance and luster of dyed silk fabrics. Domesticated silk fabrics are typically dyed with a mild acid dye or environmentally low impact fiber reactive dyes. Textile acid dye processes typically require high levels of chemicals, many of which have been classified by the Environmental Protection Agency (EPA) as being of moderate to high concern as carcinogens.  Textile acid dyeing also typically discharges large amounts of contaminated waste waters that require treatment. Low impact fiber reactive dyes have a much smaller environmental footprint but still create some health problems for the chemically sensitive.

Wild silks and spun silks are harder to clean and bleach before dyeing and dyes do not take as well requiring heavier dyeing and more chemical processing before dyeing. If you wish to avoid dyes, your options are raw silk, natural undyed silk or golden hued Muga silk.

Weighted Silk. “Weighting” is a textile manufacturing practice peculiar to and particular to silk manufacturing and involves the application of metallic salts to add body, luster and physical weight to silk fabric. The reason for adding metals to silk fabric is to increase the weight of the fabric and, because silk fabric sells by the pound, the extra weight increases the selling price of the fabric. Generally, only the finer and more expensive reeled silks are weighted rather than the less costly spun silks. Some of the different salts of metals used to weight silk include chromium, barium, lead, tin, iron and sodium magnesium.

Weighting can increase the weight of a pound of raw silk by three, four, fivefold or more. Silk can be weighted because it is highly absorptive and the metal salts are easily absorbed into the silk fibers. Silk was originally weighted to make up for the loss of weight caused by degumming which removes the sericin reducing the weight of silk by about 20 percent. Silk is one of the strongest natural fibers but the metals used to weight silk cause it to lose much of its strength and durability if the weighting is not done properly. When shopping for silk, ask if the silk is weighted silk or pure-dyed silk. Pure-dyed silk is just colored with dye and not weighted. The metallic salts used to weight silk can cause health risks and problems for some people.

Finishing Silk. The purpose of the fabric finishing process is to give the fabric its final desired feel, appearance and care properties. A variety of environmental and health hazards can be introduced during the finishing phase of silk fabrics and garments. Water-soluble substances such as starch, glue, gelatin and even sugar are sometimes used to finish silk and provide extra body to the fabric.

Silk creases and wrinkles easily, especially when damp or wet. Some silk clothing manufacturers apply softeners, elastomers, and synthetic resins such as EPSIA – a silicone-containing epoxy crosslinking agent – to increase the dry and wet anti-wrinkling and crease-resistance performance of silk garments. With the family of silicone epoxy crosslinking agents (EPSIA, EPSIB and EPTA) this crease resistance occurs because chemical cross links occur between the silk fibroin strand and the epoxy groups. Research by Zaisheng Cai and Yiping Qiu in the Textile Research Journal (January 2003) reported “in conventional epoxide finishing of silk, organic solvents have to be used, which may be hazardous to the health of the exposed workers as well as the environment.”

Chemical treatments are also added to silk to improve anti-static, water and oil repellency, flame retardant, dimensional stability and other wash-and-wear properties that our easy-care culture seems to expect. Textile chemicals have become an integral and important component of conventional textile and clothing manufacturing. Textile chemicals, also know as textile auxiliaries, have two primary purposes: to increase the efficiency and lower the costs of conventional textile manufacturing; and to create special finishing effects and properties for the clothing.

The first category of textile auxiliaries and chemicals to improve manufacturing efficiencies are used in the spinning, weaving, scouring, bleaching and dyeing processes. Textile manufacturers claim that these textile chemicals can all be washed and removed from the final garments and are used to save time, reduce labor costs and reduce material costs. Environmental impact is seldom considered, especially in garment factories in developing countries, and many of the chemicals are discharged as untreated waste waters into rivers and ground water supplies.

The second category of textile chemicals are used mostly in the fabric and garment finishing processes and are intended to be permanent. These textile auxiliaries are supposed to give clothing special properties such as a smooth silky feel, easy care, mildew resiliency, flame retardant, and easy wear. Many of these chemicals are also toxic and suspected carcinogens.

So what’s the silk consumer to do? Caveat Emptor – Latin for “Let the buyer beware" - should be your guiding principal for evaluating all fabrics and clothing. Knowledge and information are your only resources when every emotional fiber screams out “I must have that Silk Chiffon Tie Neck Blouse ($198) from Brooks Brothers!” The warp and weft of silk fashion is emotion and compromise.

If your primary concern is healthy and organic silk then consider raw silk, noil silk, Muga silks or Eri silks that are undyed or dyed with low-impact, fiber-reactive dyes. The silk fabric should not be weighted or have any easy care or protective finishes. Silks produced in small villages by local weavers are usually the most pure.

If you are concerned about the ethics of silk raising then choose wild silk, spun silk or Eri silks which do not destroy the silk worm to harvest the silk cocoons. Also ask if the silk garments were produced according to Fair Trade principles which protect the workers involved in all phases of producing the clothing.

If you are concerned about sustainable and eco-friendly silk, then seek silks dyed using low-impact and fiber reactive dyes or vegetable dyes without any finishes. Handloomed silks are the most energy-neutral.  Silk is also biodegradable and will decompose gracefully in landfills.  Although, given its durability, silk is ideal for recycled ecofashion.  NGO's and organizations such as the Institute for the Conservation of Tropical Environments are developing programs to assist poor rural communities in conservation efforts and economic development by developing their wild silk industries.

Good Luck and Enjoy.

Michael